1. Field of the Invention
The present invention relates to an image forming apparatus.
2. Description of the Related Art
Conventionally, image forming apparatuses such as copying machines temporarily store entire image data for image formation in a memory and then perform image formation using the stored image data. In this case, in order to realize a function of processing data on plural pages of a document (sorting function, for example), storage capacity for the plural pages is necessary. However, in image forming apparatuses with small storage capacity, the number of pages allowed for accumulation is limited, so that an image forming process may be aborted due to an excess of data while the document is being read. Thus, a function such as the sorting function is not effectively realized. In other words, even when the document is read, a request from a user may not be satisfied after all (sorting is not supported for all the pages of the document, for example).
In view of this, conventionally, various types of inventions have been made so as to efficiently use the small storage capacity of the image forming apparatuses
Patent Document 1 discloses a technology of an image forming apparatus in which operating efficiency is improved using a memory for compression and a page memory. When a document is read, data compressed with a predetermined compression ratio is stored in the memory for compression and uncompressed data is stored in the page memory. Patent Document 1 is intended to improve the operating efficiency by compressing data again with a higher compression ratio and storing the compressed data in the memory for compression again without returning the read document when available capacity of the memory for compression becomes not more than a predetermined value (hereafter referred to as full memory).    Patent Document 1: Japanese Laid-Open Patent Application No. 2003-152955
However, in low-priced apparatuses, it is impossible to employ plural memories as disclosed in Patent Document 1: Japanese Laid-Open Patent Application No. 2003-152955 and it is impossible to prevent a reduction of operating efficiency resulting from the full memory.